Dynamics of Resolved Turbulence in Large Eddy Simulations of Hurricanes

Abstract:

This study examines the effects of resolved turbulence in large eddy simulations (LES) of idealized hurricanes using horizontal grid spacing as small as 31 m. Resolved turbulence is defined here as the model-produced fluctuations from the azimuthal-average (i.e., mesoscale) flow of the hurricane. The distribution of resolved turbulence kinetic energy (TKE) compares well with recent airborne-radar-based studies that show a maximum of TKE at the eye-eyewall interface, especially below 2 km ASL and just inward of the radius of maximum winds. Compared to the parameterized TKE in the model, the magnitude of resolved TKE is typically more than an order of magnitude larger except (as expected) very near the surface. The resolved TKE budget further shows that TKE mean-flow advection, pressure-interaction term, and eddy transport terms are not negligible, as surmised in recent observations-based studies that could not measure these terms. Budgets of angular momentum, and moist entropy are also analyzed and compared with recent modeling studies that rely entirely on parameterized turbulence. The LES output supports previous studies in the sense that turbulence acts primarily to reduce the radial gradients of both angular momentum and moist entropy in the eyewall of simulated hurricanes.